How do we know our caffeine limit?

NEW YORK — Men may be able to handle alcohol better than women, but that doesn’t necessarily hold true for caffeine, researchers say.

Some people are sensitive to the small amounts of caffeine in decaf, says Bruce Goldberger, director of toxicology and a professor at University of Florida, where others can handle large amounts with no problem.

There’s no formula, says Laura Juliano, an assistant professor in psychology at American University; someone cannot take gender, age, race and body mass index, plug it into an equation and figure out her limit.

However, Juliano says recent studies suggest that genes may play a role in how the body responds to caffeine. Other factors, such as whether someone is a smoker or takes birth control pills, can influence it as well.

“Birth control pills slow the metabolism of caffeine,” she says. “Therefore, someone may feel the effects of caffeine more intensely when on birth control.

“On the other hand, in general smokers metabolize caffeine two times as fast as people who don’t smoke. They are less likely to feel the negative effects of caffeine.”

Once consumed, caffeine is absorbed into the bloodstream, and distributed throughout the body, says Roland Griffiths, professor of behavioral biology at Johns Hopkins University School of Medicine. He says caffeine increases urine output, opens lungs passages, and acts as a stimulant in the brain, giving us that feeling of wakefulness, or when we have had too much, the jitters.

The general recommendation is that people limit caffeine to 400 mg a day — or 300 mg for a pregnant woman or a woman who is trying to get pregnant, says Juliano. She says people can generally feel “pleasurable effects” from an amount ranging from 20 mg to 200 mg in one sitting. An 8-ounce cup of coffee has anywhere from 75-300 mg.

Children and teens should not consume a lot of caffeine, says registered dietitian Joan Salge Blake, who worries that they are replacing the more nutritious milk with sodas, energy drinks and sugary coffees.

“It is not an essential nutrient,” she says.

Like alcohol, the more one drinks, the more one needs to consume to get the same results.